1. Field of the Invention
This invention relates to methods and devices for use in telecommunications. More particularly, the invention relates to telecommunication methods and devices in which DTMF (Dual-tone, multi-Prequency tones are used to represent alpha-numeric characters. The specific and major application intended for the present invention is tone telecommunications for the deaf and hearing impaired.
2. Description of Background Art
It is estimated that there are two hundred and twenty thousand deaf and hearing impaired people in California alone, and over five million such people in the United States. There are presently existing devices on the market which permit deaf and hearing impaired people to communicate by telephone. However, those presently existing devices are not entirely adequate for serving the needs of the deaf and hearing impaired population, for reasons which will now be described.
The two most frequently used types of TDD's (telecommunication devices for the deaf) currently available require both the deaf user and the caller to possess a TDD. Presently available TDD's have the general appearance of a typewriter with a phone cradle on which a telephone handset may be placed. The phone cradle comprises the input/output portion of a part of the TDD called an acoustically coupled modem. The modem permits electrically generated, audible signals which are used by the TDD to send messages to be coupled into the microphone portion of the telephone handset. There the acoustic signals are converted into electrical signals for transmission over the telephone lines. In addition to its transmission function, the modem processes received signals. In this mode, the modem reconverts electrical signals received over the telephone line and converted to audible signals in the receiver of the telephone handset into electrical signals utilized by the TDD to produce visual messages on a TV-like display screen. Deaf people using the TDD view messages displayed on the screen, and can type an answering message by using the TDD typewriter.
Existing TDD's are expensive, costing between three hundred and seven hundred dollars each, with an average price of approximately five hundred dollars. Moreover, both the deaf party and any party wishing to communicate with him via a TDD must have their own TDD. Thus, the minimum capital outlay to permit communication via existing TDDs is approximately one thousand dollars.
A possible disadvantage of using TDDs is pointed out by Suzette Schuster, a telephone worker for the hearing impaired who states: "(the deaf)....are afraid they'll lose their speaking skills if they use TDDs." So, although existing TDDs are useful to the deaf community, as well as having applications in a number of emergency services, those considerations mentioned above limit their more extensive use by the deaf and hearing impaired population.
In an apparent effort to provide alternate methods of telecommunications for the deaf and hearing impaired, a substantive amount of inventive activity has been undertaken. The United States patents described below are evidence of that inventive activity.
Chieffo, in U.S. Pat. No. 3,585,303, June 15, 1971, discloses an instrument which converts standard electrical telephone signals into flashing light signals. These may be used by a deaf person to receive very rudimentary communications provided the caller has been appraised of the coding system to be used. An oscillator controlled by a telegraph key produces tones which permit flashing lights at another deaf person's station equipped with the apparatus to communicate Morse code messages.
Meyer, in U.S. Pat. No. 4,012,599, March 15, 1977, discloses a telephone communications system for the deaf which utilizes a standard 12 or 16 pushbutton telephone to transmit signals which are decoded and displayed as an alpha numeric message to a deaf person. The system employs a coding scheme, which must be learned by the signal transmitter, requiring two keystrokes for each letter, and 4 keystrokes for numbers and other symbols.
Coles, in U.S. Pat. No. 4,191,854, March 4, 1980, discloses an apparatus for converting sequences of standard DTMF tones, keyed in according to a pre-determined coding sequence, into LED display characters. For example, one actuation of pushbutton 5 results in the display of "J", two pushes a "K" and three pushes an "L".
Perkins, in U.S. Pat. No. 4,293,855, Oct. 6, 1981, discloses a communication device for use by handicapped persons. A keyboard switch or feedback switch operated by body movement selects and displays a desired sequence of characters or messages.
Messina, in U.S. Pat. No. 4,307,266, Dec. 22, 1981, discloses a communication device coupled to a standard telephone which has an alpha-numeric rotary dial or push-button keyboard. A code requiring two consecutive push button entries or rotary dial actuations is utilized to send signals representing letters or numbers over standard telephone lines. A decoder at the receiving telephone station converts the sequence of two-digit coded character signals into an alphanumeric display message for the deaf, or a synthesized speech signal for those who can hear.
Underkoffler, in U.S. Pat. No. 4,426,555, Jan. 17, 1984, discloses a DTMF-tone system for communicating messages by telephone to hearing impaired person. The system employs the sequential actuation of two keys of a standard 12-tone DTMF-tone key pad to transmit each character in a message. Pressing one of the first nine buttons in the key pad signifies which group of three characters is to be transmitted. Pressing keys 10, 11 or 12 signifies that the character desired is the first, second or third, respectively, in the group. Decoding logic at the receiving telephone assembles the sequence of two consecutive DTMF tones into a sequence of characters which are displayed visually in serial fashion to form a message for the hearing impaired.
Tsakanikas, in U.S. Pat. No. 4,427,848, Jan. 24, 1984, discloses use of a sequence of actuations of DTMF-tone signals to represent alpha-numeric characters. In one mode, alphabetic characters are transmitted by depressing a designated key (e.g., *) a number of times equal to the relative position of the inscription of the character on the key (i.e., the placement division of the alphabetic character), followed by the depression of the key on which the character is inscribed. In another mode, an alphabetic character is represented by depressing the particular key on which the character is inscribed a number of times equal to the placement division of the character.
The foregoing patents disclose systems for communications with deaf persons which employ DTMF-tone or rotary dial telephones. Each of the systems disclosed requires the use of two to four keystrokes to transmit each character in a sequence of characters conveying a message. Moreover, each of the systems disclosed requires the sender to learn a more or less complicated coding scheme to transmit characters. The present invention overcomes some of the disadvantages inherent in prior existing TDD devices, as will become apparent from a reading of the description of the present invention which appears below.